1. Field of the Invention
This invention relates generally to methods of providing input to a touchpad. Specifically, the invention relates to a method of detecting and tracking multiple objects on a touch sensitive surface by treating the multiple objects as a single object whose perimeter or end-points are defined by the multiple objects, thereby treating the multiple objects as a single object in order to simplify detection and tracking algorithms.
2. Description of Related Art
As portable electronic appliances become more ubiquitous, the need to efficiently control them is becoming increasingly important. The wide array of portable electronic devices that can benefit from using a touch sensitive surface as a means of providing user input include, but should not be considered limited to, music players, DVD players, video file players, personal digital assistants (PDAs), digital cameras and camcorders, mobile telephones, laptop and notebook computers, global positioning satellite (GPS) devices and other portable electronic devices. Even stationary electronic appliances such as desktop computers can take advantage of an improved system and method of providing input to a touchpad that provides greater functionality to the user.
One of the main problems that many portable and stationary electronic appliances have is that their physical dimensions limit the number of ways in which communicating with the appliances is possible. There is typically a very limited amount of space that is available for an interface when portability is an important feature. For example, mobile telephones often referred to as smart phones are now providing the functions of a telephone and a personal digital assistant (PDA). Typically, PDAs require a significant amount of surface area for input and a display screen to be practical.
A recent entry to the mobile telephone market provides an LCD having touch sensitive screen capabilities. With a finite amount of space available for a display screen space because the smart phone is portable, a means was created for expanding and shrinking the relative size of the data being displayed. More specifically, consider a page of data that if displayed at a more conventional resolution would fill a page that is approximately the size of a normal sheet of paper. The entire page of data can be shown on the display screen but in a significantly reduced size because the physical dimensions of the display screen are small compared to the size of the typical sheet of paper. The problem was how to display the data on the page at a size that was usable. The solution was to magnify smaller portions of the page. Thus, only a portion of the whole page could be viewed at any one time. The effect was to zoom in or magnify portions of the page. The tradeoff is that the entire page cannot be viewed at the same time. Accordingly, the user must move or “drag” the data on the page so that different portions of the page are revealed.
Thus, consider an entire web page being displayed so that the entire screen is visible, but the physical size of the display screen is only a matter of inches on each side. The data on the page is typically illegible at such a small size. A user will select a portion of the page to be magnified. As the data on the page grows larger and larger, the outer edges of the page essentially disappear beyond the borders of the display screen. The user then drags a finger on the display screen, thereby changing what portion of the page is visible on the display screen. Accordingly, previously hidden portions of the page become visible as other portions become hidden.
One motion that can be performed on a touch sensitive surface such as touchscreen or touchpad to perform zooming in and out of a page is a pinching motion or its reverse. For example, to perform a zoom operation to magnify the page, a user brings a thumb and forefinger together until they are touching, then places the thumb and finger down on the touch sensitive surface so that a side of the thumb and finger make contact with the touch sensitive surface. The user then essentially spreads the thumb and forefinger apart from each other while maintaining contact with the touch sensitive surface. The magnification of the page on the display screen increases as long as the thumb and forefinger continue to move apart. Similarly, the magnification of the page on the display screen is reversed by simply pinching the thumb and forefinger together while maintaining contact with the touch sensitive surface. The user can make this pinching and reverse pinching and motion repeatedly, thereby causing the page to zoom in or out as the magnification increases or decreases.
Disadvantageously, one method that is well known in the prior for performing the detection and tracking of the thumb and forefinger on the touchpad surface is to detect and track the thumb and forefinger (or whichever digits are being used to pinch and reverse pinch) as separate objects on the touch sensitive surface. Tracking multiple objects means that the calculations that are performed for one object must be performed for each object. Thus, the calculation burden on any touchpad processor increases substantially for each finger or pointing object (hereinafter used interchangeably) that is being tracked.
It would be an improvement over the prior art to simplify the process of detecting and tracking multiple objects on a touch sensitive surface such as a touchpad or a touchscreen (referred to hereinafter as a touchpad). It would be an improvement over the prior art to simplify the process of detection and tracking of multiple objects on a touch sensitive surface such as a touchpad or a touchscreen.
It is useful to describe one embodiment of touchpad and touchscreen technology that can be used in the present invention. Specifically, the capacitance-sensitive touchpad and touchscreen technology of CIRQUE® Corporation can be used to implement the present invention. The CIRQUE® Corporation touchpad is a mutual capacitance-sensing device and an example is illustrated in FIG. 1. The touchpad can be implemented using an opaque surface or using a transparent surface. Thus, the touchpad can be operated as a conventional touchpad or as a touch sensitive surface on a display screen, and thus as a touch screen.
In this touchpad technology of Cirque® Corporation, a grid of row and column electrodes is used to define the touch-sensitive area of the touchpad. Typically, the touchpad is a rectangular grid of approximately 16 by 12 electrodes, or 8 by 6 electrodes when there are space constraints. Interlaced with these row and column electrodes is a single sense electrode. All position measurements are made through the sense electrode. However, the row and column electrodes can also act as the sense electrode, so the important aspect is that at least one electrode is driving a signal, and another electrode is used for detection of a signal.
In more detail, FIG. 1 shows a capacitance sensitive touchpad 10 as taught by CIRQUE® Corporation includes a grid of row (12) and column (14) (or X and Y) electrodes in a touchpad electrode grid. All measurements of touchpad parameters are taken from a single sense electrode 16 also disposed on the touchpad electrode grid, and not from the X or Y electrodes 12, 14. No fixed reference point is used for measurements. Touchpad sensor control circuitry 20 generates signals from P,N generators 22, 24 (positive and negative) that are sent directly to the X and Y electrodes 12, 14 in various patterns. Accordingly, there is typically a one-to-one correspondence between the number of electrodes on the touchpad electrode grid, and the number of drive pins on the touchpad sensor control circuitry 20. However, this arrangement can be modified using multiplexing of electrodes.
The touchpad 10 does not depend upon an absolute capacitive measurement to determine the location of a finger (or other capacitive object) on the touchpad surface. The touchpad 10 measures an imbalance in electrical charge to the sense line 16. When no pointing object is on the touchpad 10, the touchpad sensor control circuitry 20 is in a balanced state, and there is no signal on the sense line 16. There may or may not be a capacitive charge on the electrodes 12, 14. In the methodology of CIRQUE® Corporation, that is irrelevant. When a pointing device creates imbalance because of capacitive coupling, a change in capacitance occurs on the plurality of electrodes 12, 14 that comprise the touchpad electrode grid. What is measured is the change in capacitance, and not the absolute capacitance value on the electrodes 12, 14. The touchpad 10 determines the change in capacitance by measuring the amount of charge that must be injected onto the sense line 16 to reestablish or regain balance on the sense line.
The touchpad 10 must make two complete measurement cycles for the X electrodes 12 and for the Y electrodes 14 (four complete measurements) in order to determine the position of a pointing object such as a finger. The steps are as follows for both the X 12 and the Y 14 electrodes:
First, a group of electrodes (say a select group of the X electrodes 12) are driven with a first signal from P, N generator 22 and a first measurement using mutual capacitance measurement device 26 is taken to determine the location of the largest signal. However, it is not possible from this one measurement to know whether the finger is on one side or the other of the closest electrode to the largest signal.
Next, shifting by one electrode to one side of the closest electrode, the group of electrodes is again driven with a signal. In other words, the electrode immediately to the one side of the group is added, while the electrode on the opposite side of the original group is no longer driven.
Third, the new group of electrodes is driven and a second measurement is taken.
Finally, using an equation that compares the magnitude of the two signals measured, the location of the finger is determined.
Accordingly, the touchpad 10 measures a change in capacitance in order to determine the location of a finger. All of this hardware and the methodology described above assume that the touchpad sensor control circuitry 20 is directly driving the electrodes 12, 14 of the touchpad 10. Thus, for a typical 12×16 electrode grid touchpad, there are a total of 28 pins (12+16=28) available from the touchpad sensor control circuitry 20 that are used to drive the electrodes 12, 14 of the electrode grid.
The sensitivity or resolution of the CIRQUE®Corporation touchpad is much higher than the 16 by 12 grid of row and column electrodes implies. The resolution is typically on the order of 960 counts per inch, or greater. The exact resolution is determined by the sensitivity of the components, the spacing between the electrodes on the same rows and columns, and other factors that are not material to the present invention.
Although the CIRQUE® touchpad described above uses a grid of X and Y electrodes and a separate and single sense electrode, the sense electrode can also be the X or Y electrodes by using multiplexing. Either design will enable the present invention to function.
The underlying technology for the CIRQUE® Corporation touchpad is based on capacitive sensors. However, other touchpad technologies can also be used for the present invention. These other proximity-sensitive and touch-sensitive touchpad technologies include electromagnetic, inductive, pressure sensing, electrostatic, ultrasonic, optical, resistive membrane, semi-conductive membrane or other finger or stylus-responsive technology.
The prior art includes a description of a touchpad that is already capable of the detection and tracking of multiple objects on a touchpad. This prior art patent teaches and claims that the touchpad detects and tracks individual objects anywhere on the touchpad. The patent describes a system whereby objects appear as a “maxima” on a signal graphed as a curve that indicates the presence and location of pointing objects. Consequently, there is also a “minima” which is a low segment on the signal graph which indicates that no pointing object is being detected.
FIG. 2 is a graph illustrating the concept of a first maxima 30, a minima 32 and a second maxima 34 that is the result of the detection of two objects with a gap between them on a touchpad.
The prior art is always tracking the objects as separate and individual objects, and consequently must follow each object as it moves around the touchpad.
It would be an advantage over the prior art to provide a new detection and tracking method that does not require the system to determine how many objects are on the touchpad surface, and yet still be capable of being aware of their presence.